---
title: Logging
description: Observe requests, responses, and validation failures with an optional logger.
type: package
package: "@zap-studio/fetch"
---

`createFetch(...)` accepts an optional `logger?: Logger` option from [`logger`](/logger). Pass one to observe request internals; omit it and nothing is logged — zero overhead.

```ts
import { ConsoleLogger } from "@zap-studio/logger";
import { createFetch } from "@zap-studio/fetch";

const logger = new ConsoleLogger({ minLevel: "debug" });
const { api } = createFetch({ baseURL: "https://api.example.com", logger });
```

## What Gets Logged

| Event                         | Level   | Context                        |
| ----------------------------- | ------- | ------------------------------ |
| A request goes out            | `debug` | `method`, `url`                |
| A 2xx response comes back     | `debug` | `method`, `status`, `url`      |
| A non-2xx response comes back | `warn`  | `method`, `status`, `url`      |
| Schema validation fails       | `error` | `url`, and `error` or `issues` |

A non-2xx response logs at `warn` instead of `debug` because it usually means something the caller should notice, even without `throwOnFetchError` turned on — without flooding `debug` output for every successful call.

## Bring Your Own Logger

Any object implementing the `Logger` interface works, so you can forward these events into an existing logging setup instead of `ConsoleLogger`:

```ts
import type { Logger } from "@zap-studio/logger";

const logger: Logger = {
  trace: (message, context) => myBackend.log("trace", message, context),
  debug: (message, context) => myBackend.log("debug", message, context),
  info: (message, context) => myBackend.log("info", message, context),
  warn: (message, context) => myBackend.log("warn", message, context),
  error: (message, context) => myBackend.log("error", message, context),
  fatal: (message, context) => myBackend.log("fatal", message, context),
};

const { api } = createFetch({ logger });
```

See [`logger`](/logger) for the full `Logger` interface and `ConsoleLogger` options.